Digital video has become increasingly important. Generally, several formats may be used when generating and processing digital video signals. One such format is called Serial Digital Video (SDV) format, which is a way of serially packaging the raw digital data from a moving picture. For instance, a digital camera could be generating images of a scene of a film using an SDV data format. There are several standards associated with SDV, such as standards 259M and 125M of the Society of Motion Picture and Television Engineers (SMPTE). These standards govern, for example, what is encompassed within the data stream, the speed of the data stream, encoding of the data.
Another popular format used when transmitting digital video is the Digital Video Broadcast-Asynchronous Serial Interface (DVB-ASI). DVB-ASI is governed by the following standard: European Committee for Electrotechnical Standardization/European Telecommunications Standardization Institute (CENELEC/ETSI) EN50083-9 (1998)—DVB-A010, Interfaces for CATV, “SMATV Headends and Similar Professional Equipement, Annex B: Asynchronous Serial Interface (ASI), the disclosure of which is incorporated by reference herein. Generally, images in SDV format are compressed through, for example, Motion Picture Expert Group (MPEG) compression standard. After compression, the MPEG data stream will be encoded in accordance with the DVB-ASI standard.
An exemplary system using these data streams is shown in FIG. 1. In FIG. 1, system 100 comprises an SDV source 110, a routing switcher 120, an SDV-to-MPEG encoder 130, a distribution amplifier 140, an MPEG-to-SDV decoder 150, and several resistors. In general, system 100 would work as follows. The SDV source 110 could be a digital television camera. The SDV source generates the digital video, encodes it into an SDV format, and sends this data stream to the routing switcher 120. The encoder 130 converts this SDV data stream to an MPEG data stream, which is also routed through the routing switcher 120 or another routing switcher (not shown). The resultant DVB-ASI signal is amplified, if desired, by distribution amplifier 140, and is then sent to the decoder 150 to be converted back to SDV, for example for display or storage. Distribution amplifier 140 is not needed but may be present in some systems. Between the distribution amplifier 140 and decoder 150, there could be any type of network, such as a wired or wireless network. In particular, satellite transmission and subsequent reception commonly occur here.
The routing switcher 120 is a programmable interconnection device. As such, it allows inputs to be routed to outputs. In this example, the routing switcher 120 connects an output of the SDV source 110 with an input of the encoder 130 and the DVB-ASI output of the encoder 130 to an input of the distribution amplifier 140. It is possible to program the routing switcher 120 to connect the output of the SDV source 110 to the input of the decoder 150 (through the distribution amplifier 140). However, because the decoder 150 works with MPEG data streams, such as DVB-ASI, and not SDV data streams, this routing would be nonsensical. Generally, the system designer ensures that signals are properly routed through the switcher.
The switcher may be thought of as providing logical connections to differential amplifiers 170. The differential amplifiers 170 provide true and compliment outputs. In the example of FIG. 1, one of the differential amplifiers 170 has SDV and inverted SDV outputs, and the other differential amplifier 170 has DVB-ASI and inverted DVB-ASI outputs.
The standards for the SDV format allow both the inverted and non-inverted signals to be used. Thus, for the example of FIG. 1, the inverted SDA signal could go to another SDV-to-MPEG encoder (not shown). The standards for the DVB-ASI format, however, do not allow the inverted DVB-ASI signal to be used. Because of this, the inverted DVB-ASI signals are discarded and are connected to ground through a resistor R, or another similarly destructive device.
While system 100 of FIG. 1, performs effectively for many applications, system 100 contains a number of inefficiencies, which, if overcome, could further improve the performance of the digital video system. Specifically, because the inverted DVB-ASI signals are connected to ground through a resistor, R, there is a loss of power and increased radiated emissions. The power in the inverted DVB-ASI signal is essentially converted to heat in the resistor, R, thereby wasting power. Also, because the resistor, R, grounds the inverted DVB-ASI signal, there are non-symmetrical outputs on the differential amplifier 170. If both signals were complementary, reduced emissions would occur because both signals would effectively cancel each other. However, in the system 100 of FIG. 1, one of the signals is sent to ground, which causes higher radiated emissions. Thus, the system of FIG. 1 causes higher-than-ideal power and emissions. What is needed therefore is a system that reduces or eliminates these problems, yet is also relatively inexpensive, simple, and easy-to-implement.